Electrosurgical coagulating and cutting instrument

ABSTRACT

An electrosurgical coagulating and cutting instrument employing pairs of clamping arms having wrist portions proximal to closing ramps and jaws and configured to close at their wrists first, then their distal tips and lastly, their heels. The instrument includes mechanisms for preventing the advancement of a cutting blade when the jaws are not closed. An actuator for closing the jaws includes an actuator handle and a drive head having teeth formed therein and a pawl mounted in the handle for engaging the teeth, these latter structures forming a ratcheting mechanism. Said mechanism is controllably releaseable.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. Ser. No. 09/390,087, filed Sep.3, 1999, now U.S. Pat. No. 6,419,675 the priority of which is claimedherein and the entire disclosure of which is incorporated herein byreference.

BACKGROUND AND SUMMARY OF THE INVENTION

This invention relates to endoscopic surgery and, in particular, to animproved electrosurgical coagulating and cutting instrument.

There are a number of endoscopic instruments having movable jaws formedat the distal ends of clamping arms which diverge distally. Closure istypically effected by distally advancing a collar or other componentover the diverging arms so as to urge the arms and jaws together.Examples of such devices are found in U.S. Pat. Nos. 5,258,006;5,445,638, 5,527,313 and 5,735,849. Relatively few of these devicesclose at their tips before fully grasping target tissue, thus making itdifficult to capture such tissue. Furthermore, the maximum width of theopening between the jaws tends to be limited by the diameter of thetubular sheath housing the movable components of such instruments.Another shortcoming of the prior art involves unnecessarily complicatedratcheting mechanisms for preventing the opening of jaws once closed.Such mechanisms often provide for only coarse incremental ratcheting ofthe closure movements to the jaws. Yet another shortcoming of prior artdevices is that those containing cutting elements lack sufficientprotection against unintended advancing of the cutter when the jaws areopen, thereby creating the danger of unintentionally lacerating tissuein the vicinity of the jaws. Also, many prior art devices are notconfigured to prevent the cutter from protruding outside the limits ofthe jaw envelope when the jaws are closed. Again, this shortcomingresults in the danger of causing unintentional lacerations of tissue inthe vicinity of the jaws. The invention described herein addresses theseand other shortcomings of the prior art.

SUMMARY OF THE INVENTION

In one aspect, the subject invention is comprised of a tubular sheathhaving an actuator on its proximal end and movable jaws protruding fromits distal end, the jaws being a portion of clamping arms anchoredwithin the sheath, each arm having a ramp proximal to the jaw and awrist proximal to the ramp. The clamping arms are closed by the distalmovement of a drive chassis having camming surfaces at its distal endwhich engage the ramps so as to urge the arms together, the arms beingso configured that, as they are urged together, they meet first at theirwrists, then at their distal tips and, lastly, at their heels. In apreferred embodiment of the invention, two pairs of clamping arms withmovable jaws are provided and the camming surfaces at the distal end ofthe drive chassis are formed as distal plug components having lugsextending between the pairs of clamping arms so as to maintain theproper alignment of the arms during use of the instrument.

In another aspect, the subject invention is comprised of a tubularsheath having a handle including a drive head movable between a jawsopen position and a jaws closed position, at least one pair of clampingarms, each arm including a jaw, the clamping arms and jaws being movablerelative to one another between an open position and a closed position,a drive chassis disposed within the sheath and serving to open and closethe jaws in response to movement of the drive head and a ratchetcomprising a series of teeth formed on the head and a pawl mounted inthe handle for engaging the teeth.

In another aspect, the invention is comprised of a tubular sheath havinga handle on its proximal end, including a drive head operable betweenpositions corresponding to the jaws being opened and closed, two pairsof clamping arms in a spaced-apart, parallel relationship, a drivechassis operably positioned between the driving head and the clampingarms to effect closure of the arms and their associated jaws, a surgicalcutter disposed between the pairs of arms, a drive rod operativelycoupled to the cutter on its proximal end and operatively associatedwith a drive plate at its proximal end, the plate being operable toadvance the rod and cutter, said plate being disposed proximallyadjacent the head so as to be blocked in its movement toward the cutteradvanced position when the head is not in its jaws closed position.

In yet another aspect, the invention is comprised of a method of closingthe jaws of one or more pairs of clamping arms, the method involvingsecuring relatively elongate clamping arms at their proximal end to theouter sheath of an endoscopic surgical instrument, said arms having jawsat their distal ends, ramps proximal to the jaws and wrists proximal tothe ramps. This closure method further involves advancing cammingsurfaces distally along the ramps so as to urge the arms together, theconfiguration of the arms being such that they meet first at theirwrists, then at the distal tips of the jaws and lastly at the heels ofthe jaws.

In yet another aspect, the method of this invention involves the use oftwo pairs of arms having jaws at their distal ends, ramps proximal tothe jaws and wrists proximal to the ramps as well as a surgical cutterdisposed between the pairs of arms for reciprocating longitudinalmovement between an advanced position for cutting tissue between thejaws and a retracted position in which the cutter is proximal to theheels of the jaws. This method further involves urging the jaws togetherwith camming surfaces advanced against the ramps so as to cause the armsto meet first at their wrists, then at the distal tips of the jaws andlastly at the heels of the jaws following which electrosurgical energyis provided to the jaws so as to coagulate tissue captured therein.After coagulation, the cutter is advanced so as to cut tissue capturedbetween the pairs of jaws. During actuation, the appropriate separationand alignment of the jaws may be maintained by the use of lugs disposedbetween the corresponding arms of adjacent jaw pairs.

In yet another aspect, the invention involves the method of providingfor a ratcheted closure sequence in which an actuator handle is used toeffect closure, said actuator handle having a drive head with teethformed thereon for engagement with a pawl. In a preferred method, thepawl is comprised of two tines of unequal length so as to provide forfiner ratcheting with teeth of a given size than would otherwise bepossible with a single tine or tines of equal length.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an instrument embodying the subjectinvention.

FIG. 2 is an enlarged perspective view of a distal portion of theinstrument with parts of the outer sheath broken away.

FIG. 3A is an exploded view of the parts shown in FIG. 2.

FIG. 3B is a detailed assembly drawing of selected components depictedin FIG. 3A.

FIG. 4 is a perspective view of the handle of an instrument embodyingthe invention, partly in section, with the left side of the housingremoved.

FIGS. 5 and 6 are left-side elevations with the left side of the housingremoved, partly in section, showing the operation of certain componentscontained within the handle of the instrument.

FIGS. 7A–E are a series of side elevations showing the closure sequenceof the clamping arms and their jaws as well as the movement of thecutter of the instrument. In FIG. 7E, the two jaws closest to the viewerhave been removed in order to more clearly show the cutter.

FIG. 8 is a schematic diagram showing a preferred way in which theclamping arms of the invention can be energized for electrosurgical use.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the general arrangement of a preferred embodiment of theelectrosurgical coagulating and cutting instrument 10 of this invention.Tubular sheath 12 extends proximally into handle 14 and has a distal end11. Jaws 16, 18, 20 and 22 (see FIG. 2) protrude beyond the distal end11 of sheath 12. Jaws 16, 18, 20 and 22 are electrically isolated andmay be connected to an electrosurgical generator by means of cable 26.Mounted on a distal portion of handle 14 is a rotation knob 32 which, asexplained below, is used to rotate sheath 12 along with jaws 16, 18, 20and 22 with respect to handle 14. A jaw actuator 27 is mounted on axle130 on handle 14. As explained below, when actuator handle 24 is graspedand moved toward stationary grip 25, jaws 16, 18, 20 and 22 will beclosed. The closure action of the jaws can be controlled by a ratchetmechanism which, in turn, is selectively engaged or disengaged by movingratchet control 30 up or down. Ratchet control 30 is convenientlylocated for operation with the surgeon's thumb.

Also seen in FIG. 1 is the tip of surgical cutter 34. As explainedbelow, cutter 34 may be advanced distally by operation of a cutteradvance control in the form of ear 28. A stop 29 is provided to limitthe distal movement of blade 34. Again, ear 28 is conveniently placedfor operation by the surgeon's thumb. A corresponding ear is desirablyplaced on the right-hand side of instrument 10 for additionalconvenience.

Referring now to FIGS. 2 and 3A, it will be seen that a preferredembodiment of the invention may include four clamping arms 15, 17, 19and 21. Arms 15 and 17 constitute a pair arranged in opposed relation toeach other. Likewise, arms 19 and 21 constitute another pair in the samerelationship. Pair 15, 17 and pair 19, 21 are in a parallel,spaced-apart relationship, as shown in FIG. 2. As also shown in FIG. 2,surgical cutter 34 passes through sheath 12 between clamping arm pairs15, 17 and 19, 21.

Clamping arms 15, 17, 19 and 21 are secured to sheath 12 by means of anarm anchoring fixture 44 and centering members 46. Sheath 12 is made ofany suitably rigid material such as metal or plastic. If made of metal,sheath 12 is preferably spray coated with an insulating material such asa polyurethane to provide electrical isolation between the sheath andthe patient's body. Fixture 44 and members 46 are preferably made of anonconducting material such as a plastic having suitable mechanicalproperties for their indicated purpose.

Anchoring fixture 44 is secured in sheath 12 by means of pins 42 whichpass through sheath 12 and are press-fitted into holes 43 (see FIG. 3A)in fixture 44. Although not shown, similar pins and holes are providedon the underside of the instrument to provide additional security. Toprevent longitudinal movement of arms 15, 17, 19 and 21 with respect tosheath 12, the arms are provided with indentations 50 which engage lugs54 on fixture 44. The proximal ends 52 of arms 15, 17, 19 and 21 areprovided with apertures 53 (see FIG. 7A) to facilitate attachment ofelectrical wires for connection to an electrosurgical unit. Anuninsulated or “stripped” end of an insulated wire (not shown) canconveniently be threaded through an aperture 53, twisted around itself,soldered and then covered with a shrink-wrapped insulating material. Itis important that the wires connected to ends 52 be kept electricallyisolated from one another so as to prevent shorting between themselvesor with other components of the instrument. Other methods of wireattachment may be used. For example, it would be possible to create apin and socket arrangement in which ends 52 would be formed as pins andsockets would be fixed to the ends of the wires.

Referring again to FIGS. 2 and 3A, clamping arms 15, 17, 19, and 21 areelectrically isolated from one another by means of an insulating coating(not shown) such as a thin layer of polyurethane. Such a coating may beapplied by any conventional process such as spray coating. Tissuegrasping surfaces 74, 76, 78 and 80 (see FIG. 3A) of arms 15, 17, 19 and21 are not coated, however. This permits these surfaces to grasp tissueand to transmit electrosurgical energy through such tissue forcoagulation purposes.

Also shown in FIGS. 2 and 3A is a plastic sealing disk 48 having acentral opening 49 and a side opening 51. Disk 48 is intended to preventthe passage of gas or fluids from the distal end of the instrumentthrough sheath 12. Disk 48 is thus sized to be in intimate contact withthe interior of sheath 12. Central opening 49 matches thecross-sectional shape of anchoring fixture 44, thus allowing disk 48 tobe tightly fit on the proximal end of fixture 44. Disk 48 is alsoprovided with a side opening 51 through which the spine 45 of drivechassis 39 may pass, as explained below.

FIG. 3B shows the manner in which sheath 12, drive chassis 39, drive rod58 and cutter 34 are assembled. Drive chassis 39 is made of stainlesssteel and is comprised of a spine 45 running the full length of thechassis. Chassis 39 has two “C” channels, distal “C” channel 40 andproximal “C” channel 41. Drive chassis 39 is spray coated in itsentirety with a polyurethane material having high dielectric strengthand good wear resistance. This material may be the same as that used tocoat the clamping arms 15, 17, 19 and 21 and sheath 12. Slots 47 areprovided near the proximal end of “C” channel 41 to facilitateattachment of drive collar 98 shown in FIGS. 4, 5 and 6. As best seen inFIG. 4, proximal “C” channel 41 extends into handle 14. Drive collar 98is rigidly attached to the proximal end of “C” channel 41. To facilitatethis attachment, drive collar 98 is formed in two halves which togethersurround the proximal end of “C” channel 41. Each of the halves isformed with a rib (not shown) on its inside surface to engage slot 47 of“C” channel 41 (see FIG. 3B). The two halves of drive collar 98 may beheld together by means of screws 134 or any other suitable method ofattachment. For example, another method of attachment, and one which ispreferred, is to form the two halves of drive collar 98 with mating pinsand recesses sized so that they will engage each other in a frictionalfit as they are assembled about the proximal end of “C” channel 41.

Referring again to FIG. 3B, it will be understood that in the assembledinstrument, drive chassis 39 is disposed within sheath 12. Also, it willbe appreciated that in the assembled instrument, drive rod 58 passesthrough proximal “C” channel 41 and, as shown in FIGS. 4 and 5, extendsproximally into handle 14 where shank 110 and button 108 cooperate withdrive plate 106 in a manner described below. Drive rod 58 may be made ofany suitable material such as metal or plastic.

As shown in FIG. 2, cutter 34 is of sufficient length to pass from itscutting edge 91 at the distal end of the instrument proximally betweenthe clamping arm pairs 15, 17 and 19, 21 and through a slot 56 (see FIG.3A) in fixture 44 and seal 48 after which it is attached by means of apin-type component 67 to drive rod 58. In FIG. 2, cutter 34 is shown inits retracted position. The distance from disk 48 to the distal end ofdrive rod 58 must be sufficient to accommodate the movement of cutter 34to its advanced position. Also, the distance between distal “C” channel40 and proximal “C” channel 41 (see FIG. 3B) must be sufficient oneither end of fixture 44 to accommodate the reciprocal movement of drivechassis 39 between its jaws open position and its jaws closed position.Cutter 34 is preferably made of stainless steel with a sharpened cuttingedge 91.

Referring again to FIGS. 2 and 3A, it will be seen that, in a preferredembodiment of the invention, a pair of distal plugs 36 and 38 areassembled over distal “C” channel 40. Plug 36 contains at its endssemi-circular centering collars 31 and 33. Similarly, plug 38 is formedwith collars 35 and 37. Collars 31 and 35 are formed with separationlugs 60. As seen in FIGS. 2 and 3A, the separation lugs 60 serve tomaintain the separation between the clamping arms of pairs 15, 17 and19, 21 during activation. In other words, the separation of the two topclamping arms 15 and 19 is maintained by lug 60 on plug 38 while theseparation between the bottom clamping arms 17 and 21 (see FIG. 3A) ismaintained by lug 60 on plug 36. Besides serving to keep the clampingarms centered within sheath 12, plugs 36, 38 serve on their distal endsto cam the clamping arms 15, 17, 19, and 21 together as the drivechassis 39 moves distally. In this regard, it will be seen in FIG. 3Athat clamping arms 15 and 17 include ramps 61 and 63, respectively.Similarly, clamping arms 19 and 21 include ramps 64 and 65.Semi-circular collars 31 and 35 (see FIG. 3A) engage these ramps asdrive chassis 39 moves distally. Although the instrument will functionwithout the plugs 36,38, it is preferable to include them.

FIGS. 4, 5 and 6 illustrate the mechanisms and structures used toadvance and retract the drive chassis, thus closing and opening jaws 16,18, 20 and 22. Actuator 27 is a plastic lever pivotally mounted on axle130. Axle 130 is molded as a part of actuator 27 and the right and leftsides of the housings of handle 14, also plastic, are molded with asuitable aperture into which axle 130 rotatably fits. The upper portionof actuator 27 is formed as a drive head 92 positioned adjacent chassisdrive collar 98. Spring 100 biases the drive chassis proximally to itsjaws open position. When actuator handle 24 is drawn toward stationarygrip 25, drive head 92 moves distally forcing collar 98 and drivechassis 39 to move distally. As that occurs, the centering collars 31and 35 found on the distal ends of plugs 36 and 38 (see FIG. 3A) engageramps 61, 63, 64 and 65 so as to urge the clamping arms together. One ofthe lugs 60 (see FIGS. 2 and 3A) is disposed between ramps 61 and 64while the other is disposed between ramps 63 and 65, thus serving tokeep the clamping arms properly aligned and separated during activation.

Spring 100 is disposed within cavity 102 against shoulder 104 andagainst drive collar 98. Thus, as actuator handle 24 is operated to itsjaws closed position, spring 100 is compressed. When the actuator handleis released (and pawl 96 is disengaged from teeth 94 as explainedbelow), spring 100 will drive collar 98 and drive chassis 39 proximally,thus allowing jaw pairs 16, 18 and 20, 22 to resume their open position.

The closure sequence is illustrated in FIGS. 7A–E. For the sake ofsimplicity, the distal plugs 36 and 38 are not shown. FIG. 7A shows jaws16 and 18 in their open position. As shown in FIGS. 7A and 3A, clampingarm 15 terminates in a jaw member 16 which includes a distal tip 66 anda heel 82 separated by a tissue grasping surface 74. Proximal to jaw 16is ramp 61. Proximal to ramp 61 is wrist 55. Wrist 55 is located whereclamping arm 15 begins to diverge distally from clamping arm 17. Theportion of clamping arm 15 proximal to wrist 55 is substantiallystraight until the arm begins to thicken near its proximal end 52.Clamping arm 19 is identical in configuration to clamping arm 15.Clamping arms 17 and 21 are identical in configuration but are disposedin opposed relation to clamping arms 15 and 19, respectively.

FIG. 7B illustrates that as “C” section 40 of drive chassis 39 movesdistally along ramps 61 and 63, the clamping arms are urged toward oneanother and first meet at their wrists 55 and 57. This occurs becausethe clamping arms 15 and 17 are cross-sectionally shaped so that theywill bend at flex points 115 and 117, respectively. In FIG. 7B, a bloodvessel 138 has been captured loosely between jaws 16 and 18. The nextstep in the closing sequence is illustrated in FIG. 7C. There, the drivechassis has been further advanced distally causing tips 66 and 68 tomeet. Note that heels 82 and 84 are still spaced apart. In FIG. 7D, itis seen that further distal advancement of the drive chassis results inbringing heels 82 and 84 together, thus completing the closure of jaws16 and 18.

Once closure has been completed, the jaws can be supplied withelectrosurgical energy to coagulate the tissue between them. The bipolarcoagulation process is generally known and for most applications, jaws16 and 20 (see FIG. 3A) are of one polarity while jaws 18 and 22 are ofthe other. After coagulation has occurred, cutter 34 is advanced to cutthe captured tissue. It will be appreciated that cutter 34 passesbetween jaw pairs 16, 18 and 20, 22. As shown in FIG. 7E (in which jaws16 and 18 have been removed), cutter 34 may be advanced to a point whereits distal tip is substantially aligned with the distal tips of jaws 16,18, 20 and 22. In the preferred embodiment of this instrument, cutter 34is configured so as to prevent its cutting edge 91 or any other part ofcutter 34 from protruding outside the envelope of space defined by andbetween jaw pairs 16,18 and 20, 22.

It may be noted that drive head 92 is slotted, as shown in FIG. 4 toaccommodate the passage of cutter drive rod 58. Also, drive head 92 isprovided with teeth positioned for interaction with pawl 96. Pawl 96 ismade of a molded plastic with an integral axle 112. Suitable recesses(not shown) are provided in both halves of handle 14 to receive axle112, thus permitting movement of pawl 96 into or out of engagement withteeth 94. Ratchet control 30 (see FIG. 5) engages pawl 96 with its lips126, 128. Ratchet control 30 is urged proximally by spring 122 againstthe housing of handle 14. Detent recess 124 is engaged by detent lug 125when the ratchet control 30 is moved to its lower position. In thatposition, lip 126 rotates pawl 96 about axle 112, thereby disengagingpawl 96 from teeth 94. When pawl 96 is disengaged, actuator handle 24may be freely drawn to stationary grip 25 and released as desired, thuspermitting drive chassis 39 to move reciprocally opening and closingjaws 16, 18, 20 and 22. When the pawl is engaged, as shown in FIGS. 4–6,actuator handle 24 will not return to its jaws open position. Thus, ifthe ratchet control 30 is in its upper position, drive head may not moveproximally after it has been moved distally. As seen in FIG. 4, pawl 96is comprised of a pair of tines. One tine is shorter than the other sothat they may alternately engage teeth 94 in a stepwise fashion. Thisarrangement provides for finer increments in the ratcheting operationthen would be the case if the tines were of equal length.

FIGS. 4, 5 and 6 also illustrate the structures and methods by whichcutter 34 is advanced. As noted earlier, drive rod 58 extends through“C” channel 41, drive collar 98, drive head 92 and is engaged withcutter drive plate 106. Formed in plastic, cutter drive plate 106 isintegral with axle 114 which, in turn, is driven by ear 28. Ear 28 isrigidly fixed to axle 114 and, thus, as ear 28 is rotated counterclockwise about axle 114, plate 106 is rotated correspondingly. As plate106 advances, it forces cutter drive rod 58 distally, thus advancingcutter 34. Note that shank 110 is slideably fit within the vertical slot109 (see FIG. 4) of drive plate 106. However, slot 109 is too narrow topermit button 108 or the body of rod 58 distal to shank 110 to passtherethough.

As shown in FIGS. 5 and 6, plate 106 is provided with a pair of safetyarcs 107 which are positioned to make contact with drive head 92. Onlyone safety arc 107 is visible, the other being hidden in these figures.Cutter drive plate 106 is operable between a proximal position, as shownin FIG. 5 and a distal position, as shown in FIG. 6. When plate 106 isin its proximal position, corresponding to the retracted position forcutter 34, safety arcs 107 will be in contact with drive head 92, if thehead is in its proximal position corresponding to the jaws openposition. Thus, plate 106 cannot be moved distally so as to advance thecutter. However, when actuator handle 24 is drawn to the jaws closedposition, as shown in FIG. 6, plate 106 can be moved distally, thusadvancing cutter 34. This arrangement prevents the inadvertentlaceration of tissue which might occur if the cutter 34 could beadvanced when the jaws are open.

Spring 116 has several parts, ratchet control portion 122 having beenmentioned above. Spring 116 also includes a cutter biasing section 118which, as shown in FIGS. 4, 5 and 6 serve to urge plate 106 proximally.Thus, when the surgeon releases the distal pressure on ear 28, thecutter 34 will be retracted. Spring 116 is captured within suitablerecesses formed into the right and left sides of housing 14 so as topermit the independent movements of ratchet control portion 122 andblade biasing section 118. Spacer tab 120 of spring 116 is notched outof spring 116 and serves to frictionally fit spring 116 to plate 106during assembly. Apertures for axle 114 are provided in both sides ofhousing 14. Thus, during assembly spring 116 is attached to plate 106 asindicated and axle 114 of plate 106 is inserted into its correspondingaperture. In this way, assembly of the instrument is greatlyfacilitated.

As also shown in FIGS. 4, 5 and 6, rotation knob 32 surrounds sheath 12and is tightly fitted thereto. Sheath 12 is loosely fitted withinhousing 14 so that it can be rotated by the surgeon by means of rotationknob 32. When sheath 12 is so rotated, the entire clamping and cuttingmechanism will be rotated as well due to the fact that the clamping arms15, 17, 19 and 21 are secured to sheath 12. As shown in FIG. 3B, sheath12 is provided with a slot 23 which preferably extends through 270° ofthe circumference of sheath 12. One side of handle 14 is formed with apin (not shown) positioned to protrude into slot 23, thus preventingaxial movement of sheath 12 while permitting its rotation by means ofknob 32.

As shown in FIG. 8, clamping arms 15, 17, 19 and 21 may be connected bywires 77, 79, 81 and 83, respectively to one or more electrosurgicalunits 85. These connections can be made through a switching device 87.Such an arrangement permits the clamping arms and their associated jawsto be energized with different polarity patterns. For example, arms 15and 19 can be of positive polarity while arms 17 and 21 can be negative.If arms 15 and 17 are energized by one ESU while arms 19 and 21 areenergized by a separate ESU, then the resulting heat generated in tissuecaptured between the jaws will occur primarily between those pairs ofarms. On the other hand, if arm 15 and arm 21 were to be connected toone ESU while arms 19 and 17 were to be connected to a separate ESU,then a “cross-fire” pattern of heating would occur. In that pattern,coagulating heat would be generated between arms 19 and 17 andseparately between arms 15 and 21, thus creating an “X” pattern in whichthe greatest amount of heat would occur in the middle. Anotherpossibility would be to connect arms 15 and 19 to the poles of one ESUwhile arm 17 and 21 would be connected to the poles of a separate ESU.In this configuration, coagulating heat would be generated primarilybetween arms 15 and 19 on the one hand and arms 17 and 21 on the other.These various firing arrangements can be accomplished using technologywell known to those skilled in the art. Furthermore, those skilled inthe art will appreciate that the same firing patterns can beaccomplished using a single ESU with appropriate signal splitting andswitching devices.

An advantage of the above-described instrument concerns the range ofmotion of its jaws with relation to the diameter of sheath 12. Clampingarms 15 and 17 are configured so that upon closure, they meet first attheir wrists 55 and 57. Similarly, arms 19 and 21 meet at wrists 59 and62, thus creating a relatively short cantilever beam from the wrists tothe distal tips of the clamping arms. This arrangement, in turn, permitsthe ramps 61, 63 and 64, 65 to diverge distally at a greater angle thanwould be possible if the arms were to meet first at their tips. Thus,the described arrangement permits a wider jaw opening for a given sheathdiameter. This advantage is maximized with the use of ramp notches 90which are provided in the distal end 11 of sheath 12. The distal end 11of sheath 12 is positioned proximally adjacent to the heels 82, 84, 86and 88, thus serving as a tissue stop to prevent tissue from contactingthe cutting edge 91 of cutter 34 when cutter 34 is retracted.

Those skilled in the art will appreciate that various modifications canbe made to the above-described embodiment of the subject inventionwithout departing from its essence. It is intended to encompass all suchmodifications within the scope of the following appended claims.

1. A method of closing a pair of clamping arms of an endoscopic graspingtool surgical instrument, the pair of clamping arms being anchored toand within a tubular sheath in an opposed, normally open relation to oneanother and being of the type having jaws with distal tips and heels andhaving wrists proximal to the jaws, wherein the method comprises thesteps of: urging the arms together so that they meet at their wristswhile the jaws remain open; and then urging the jaws together so thatthey meet first at their distal tips and last at their heels.
 2. Themethod of claim 1 further comprising providing a drive chassis disposedwithin the sheath, said drive chassis being operably coupled to theclamping arms for urging the arms together as the chassis movesdistally.
 3. The method of claim 2 further comprising moving the drivechassis distally using a drive head of a handle to cause the urging thearms together.
 4. The method of claim 2 wherein said drive chassiscomprises camming surfaces and said each pair of clamping arms comprisescamming ramps, and further comprising engaging said camming surfaceswith said camming ramps to cause the urging of the arms together.
 5. Themethod of claim 4 further comprising maintaining separation ofcorresponding arms of said two pair of clamping arms by positioning atleast one lug on said camming surfaces.
 6. A method of advancing asurgical cutter of an endoscopic grasping tool surgical instrumentcomprising: providing two pairs of clamping arms, the arms of each pairbeing disposed in opposed relation to each other; providing the surgicalcutter disposed between the pairs of arms and supported forreciprocating longitudinal movement between an advanced position inwhich the cutter occupies at least part of an envelope of space definedby and between two pairs of jaws of the pair of arms and a retractableposition in which the cutter is proximal to the envelope; providing ahandle having a drive head operable between a jaws open position and ajaws closed position; providing a drive rod having a distal endoperatively coupled to the cutter and a proximal end in the handle;providing a drive plate operatively coupled to the distal end of thedrive rod; moving the cutter to a cutter advanced position by moving thedrive plate; and blocking movement of the cutter to the cutter advancedposition by the drive head when the drive head is not in the jaws closedposition.
 7. The method of claim 6 further comprising providing a drivechassis having a proximal position adjacent to the drive head and beingoperably coupled to the clamping arms so as to move the jaws together asthe chassis moves distally and further comprising moving the drive headdistally to cause the drive chassis to move distally to move the jaws toa jaws closed position.
 8. The method of claim 6 further comprisingmoving the cutter to a cutter retracted position by moving the driveplate.
 9. The method of claim 6 wherein the moving the cutter to acutter advanced position comprises moving the cutter to a positionwherein a cutting edge of the cutter does not protrude outside theenvelope.
 10. A method of ratcheting the closure of a pair of jaws of asurgical instrument comprising the steps of: providing a pivotallymounted actuator handle operatively coupled to the jaws, said handlehaving a drive head which moves distally to effect jaw closure and saiddrive head having teeth formed thereon; and providing a pawl positionedfor engagement with the teeth so as to prevent proximal movement of thedrive head alter it has moved distally; wherein the pawl is comprised oftwo tines of unequal length so that each tine engages the teethalternately with the other, as the bead moves distally.